Syrio Forel: "Do you pray to the gods?"
Arya Stark: "The old and the new."
Syrio Forel: "There is only one god. And his name is death. And there is only one thing we say to death, 'Not today.' " - Game of Thrones

The Mountain and some men come to capture Arya while she is training with Syrio with wooden swords. Syrio takes out all the men except The Mountain with only a wooden sword.

Syrio Forel: "Begone now Arya."
Arya Stark: "Come with me. Run!"
Syrio Forel: "The first sword of Braavos does not run. ... What do we say to the god of death?"
Arya Stark: "Not today."
Syrio Forel: "Go." - Game of Thrones